Means for supplying power to thermionic valves



, Sept. 13,1927.

I 1,642,526 a. M. WRIGHT MEANS FOR SUPPLYING POWER TO THERIIONIG VALVESFiled Aug. 17. 1926 nmmmmm INVEN TOR.

A TTORNEY.

Patented .-Sept. 13, 1927.

UNITED STATES}- P ENT i OFFICE.

PORATION OI- AHEBICA, A CORPORATION 01 DELAWARE.

mums iron surrLYnvG rowan 'ro rr'mimromc 'vanvns.

Application filed August 17, 1929, Serial No. 129,897, and in GreatBritain August 15, 1995.

This invention relates to improved means for sup lying the high tensionpower for a thermionic valve from an ordinary power supply circuit orthe like. 5 In many cases it is desirable for practlcal reasons tosupply power from direct current generators or public supply mains, as,for example, to valves in central telegraph ofiices or to the valves ofbroadcast receivers.

When, however, power is supplied 'to the anode circuits of thermionicvalves from ordinary power supply circuits, difiiculties arise from twomain causes I (1') The fairly large semi-permanent :5 changes inthe-supply voltage w ich occur fromtime to time owing to variations 1nthe load on the feeders. These changes tend to affect the anode supplyto the .valves and may put the direct current bridges ina telegraphoflice out of adjustment.

(23 The ripples superimposed on the stea y direct current voltage, whichripples are caused by commutation and .by the armature teeth in thegenerators supplying the ."5 circuit. Such ripples give rise to a hum inthe filament, where R is the series resistance audio circuits or inbroadcast receivers.

According to the present invention potential is so applied from a powercircuit or the like to the anode and .to the grid of a thermionic valve,that when a change in the electromotive' force applied to the anodeoccurs, there will be a change of opposite effect in the electromotiveforce applied'to the grid,

the proportions between the electromotive forces applied being such thatthe effective output of the valve remains substantially constant.

In'one form of construction, suitable for use in a transformer coupledamplifier, the

40 terminals of the power supply are shunted by a resistance, and thepositive terminal is connected through the primary of the intervalvetransformer to the anode of the valve.

At a point along the resistance, a connection is taken to the filamentof the valve and the grid circuit connection-is made to the negativeterminal of the power supply. The

usual biasing battery may be included in series with the input terminal.The tapping .Q point for the filament connection is such that it dividesthe resistance into two parts, so

that the required compensating voltage is applied to the grid. I havefound that this compensation is'obtained whenthepart of the resistanceadjacent the anode is approximately 111, times that adjacent the id,where m is the magnification factor 0 With this arrangement so long asthe valve the valve.

is working on the substantially straight partof its characteristic curvemay change in the voltage applied to the am) will be compensated or by-a change of opposite effect in the voltageapplied to the grid, so thatthe effective output of the valve, which in this case isthe anodecurrent, remains substantially constant.

In a modification, suitable for use in a re-' sistance coupledamplifier, the grid circuit connection'is made to the tapping point uponthe reslstance, and the filament and anode circuit connections are madeeach to one end of the said resistance and to the-negative and positiveterminals of the power supply respectively. With this arrangement I havefound the required compensation to be obtalned and the effective outputof the valve (in this case the anode voltage) to remain substantiallunafiected byvariations in the power supp y when the part of theresistance adjacent the anode is Ra times that adjacent Any potentialdividing arrangement maybe used in place of the resistance hereinbeforereferred to. A convenient method, in

.the case where the supply is from a local motor generator or the like,is to provide an extra brush resting on the commutator thereof, whichbrush serves as the filament tapping point. This arrangement avoids thelosses which occur when resistances are used. It may be desirable toprovide condensers in shunt across the tapping points of the resistancesor the like. When such condensers are used, their impedances should bein the before-mentioned ratio.

The arrangements hereinbefore described are suitable for use with directcurrent'supply from an ordinary power circuit. If alternating currentpower supply only is available, such arrangements may conveniently beemployed in con'unction with rectifiers. "The invention is i ustrated inthe accomanying drawing, in which Figure l is a diagram of a transformercoupled amplifier, according to the invention; Figure 2 is 0. diaram ofa resistance capacity coupled 'amplifier and Figure 3 is a diagram of aresistiaince battery coupled direct current ampli- Referrin to Figure 1,V is a thermionic valve and the input terminals, whercbythe impulses tobe amplified are applied between the grid and filament of the saidvalve. T is an. output transformer, whose secondary v is connected tooutput terminals 0. M+

rent characteristic 0 and M- are the positive and negative terminals ofthe power supply, which is connected across the ends of a resistanceNFP, the part PF of which is included in the anode circuit of the valve,the part NF being included in the grid circuit thereof. B is a rid biasbattery. I have found that satisactory com ensation is obtained when theparts F, F of the resistance are so proportioned that p are where m isthe magnification constant of the valve.

It will be seen that when fluctuation, say, an increase of anodepotential, occurs, a compensating fall of grid voltageis occasioned, sothat the anode current remains substantially constant.

In Figure 2, those parts corresponding to parts shown in Figure 1 areindicated by like reference letters. G is a coupling condenser.

The arrangement shown diagrammatically in Figure 3 is suitable for useas a direct current amplifier, and is generally similar to that shown inFigure 2, except that the caacitv G (of the said Figure 2) is replaced ya batte D, whereby the grid of the succeeding va ve (not shown) can beadjusted to the correct potential.

I have found that in this case satisfactory compensation results areobtained when stir FP Ra.

when R is the anode series resistance and a is the slope of the ridvoltage-anode ourthe valve.

It will be seen, in this case, that if an increase in anode otentialoccurs, a compensating rise of grid voltage is occasioned, so that theanode potential to negative end of filament remains substantiallyconstant.

The invention is also applicable to amplitiers of the so-called chokecoupled or inductive resistance coupled type.

Having described my invention, what I claim is:

1. Means for supplying current from a power circuit to a resistancecoupled thermionic tube having cathode, anode and grid electrodes,including a resistance shunting the terminals of the power supply, and aconnection from said resistance to the grid of the tube, said connectiondividing the resistance in such a manner that one art is included in theanode circuitof said tu e and the other part included in the gridcircuit, the ratio of the resistance of the grid circuit to that in theanode circuit being equal to the reciprocal of the anode seriesresistance multiplied by the slope of the grid voltageanode currentcharacteristic of the tube.

2. The method of maintaining the anode potential of a resistance coupledthermionic valve substantially constant when the valve is receiving itspower from direct current generators subject to fluctuations. consistingin inserting resistances in the anode and grid circuits of the valve,the ratio between said resistances being equal in value to the anodeseries resistance multiplied by the slope of the grid voltage-anodecurrent characteristic of the valve by any change occurring in theelectromotive force applied to the anode will produce a correspondingchange in the electromotive force applied to the grid.

3. In an amplifier arrangement having an output circuit, a seriesresistance in the output circuit, means for supplying current from apower circuit to'said amplifier arrangement, a resistance shunting saidpower supply, the cathode of the amplifier and the output circuit beingconnected to the terminals of the shunt resistance,.and the grid of saidamplifier being tapped off from said shunt resistance at a pointintermediate of its terminals, said resistance being divided in suchmanner that the ratio of the portions included in the input and outputcireuitsis equal to the reciprocal of the anode series resistancemultiplled by the slope of the grid voltage-anode current characteristicof the amplifier.

4. The method of maintaining the potential difl'erence between the anodeand filament of an impedance coupled thermionic valve substantiallyconstant when the valve is supplied with a resistance shuntedfluctuating source of direct current which consists in includingportions of the resistance in the input and output circuits of the valvein such a manner that the ratio of the portions included in the inputandoutput circuits is equal to the reciprocal of the anode seriesresistance multiplied by the slope of the grid voltage-anode currentcharacteristic of the thermionic valve.

